1. Field of the Invention
The present invention relates to a light-emitting diode (LED) light source control method, and more particularly to a light-emitting diode light source control method used for controlling a composite and a single color LED light source.
2. Description of the Related Art
Image scanners (image scanning and reading devices) are being increasingly used for the purpose of optically reading a given objective image by use of an image sensor such as a CCD line sensor and outputting image signals to various image processing devices including a computer, a copying machine and a facsimile. A cold-cathode fluorescent lamp (CCFL), which is generally used as a light source in the image scanner, suffers the disadvantage that the cold-cathode fluorescent lamp always needs a preheating time before operation and this preheating time definitely retards the scanning speed of the image scanner. Light-emitting diodes (LED) that emit white light may be used as a replacement of the cold-cathode fluorescent lamp, but the high cost and the always-on illumination of the white light LEDs are still problems to be overcome since the always-on illumination degrades the performance of the LEDs and reduces their life times.
FIG. 1 shows a conventional light-emitting diode light source control method controlling a white light-emitting diode as a light source. As in FIG. 1, the white light LED is always turned on and most of the light energies are wasted amid any single time interval since only one channel of one color of image sensors is responsive and the data of one color are processed in one time interval.
FIG. 2 shows another conventional light-emitting diode light source control method controlling red, green and blue color light-emitting diodes as light sources. The method turns on the red color light-emitting diode and processes the data generated by the illumination of the blue color light-emitting diode during time interval T1. Then the red color light-emitting diode is tuned off and the green color light-emitting diode is turned on and the data generated by the illumination of the red color light-emitting diode during time interval T2. Next the green color light-emitting diode is turned off and the blue color light-emitting diode is turned on and the data generated by the illumination of the green color light-emitting diode during time interval T3. This method is apparently more complex and presents more cost since more kinds of light-emitting diode and control circuits are involved.
In view of the drawbacks related to the prior art, there is a continued need to develop a new light-emitting diode light source control method that overcomes the disadvantages associated with the prior art. The requirements of this invention are that it solves the problems mentioned above.